Reciprocating machine with two sub-chambers

ABSTRACT

A reciprocating machine includes a housing ( 12 ) and piston means ( 20 ) that are cyclically relatively displaceable along an axis ( 11 ) to define a variable volume working chamber ( 50 ). There is further provided air inlet means and fuel inlet means ( 100 ) admitting air and fuel to the working chamber for forming an ignitable mixture after compression of the air therein, and means to exhaust combustion products from the working chamber. The variable volume working chamber ( 50 ) includes at least two sub-chambers, a combustion chamber ( 54 ) and a main chamber ( 52 ) mutually displaced on the axis ( 11 ) and in communication at a cross section ( 53 ) at which gas in the combustion chamber ( 54 ) may expand at least partially laterally as it flows from the combustion chamber ( 54 ) into the main chamber ( 52 ). The air admission means, the exhaust means and the chambers ( 52, 54 ) are arranged so that a swirl of gas is generated and maintained about the axis ( 11 ) in both chambers ( 52, 54 ) during operation of the machine.

FIELD OF THE INVENTION

This invention relates generally to reciprocatory machines, includingthose operable as internal combustion engines, but in a particularlypreferred embodiment relates to an improved sleeve valved engine.

BACKGROUND ART

In recent decades, substantial research effort has been expended on aquest for a commercially practical adiabatic engine. A useful referenceon the topic is “The Adiabatic Engine”, published by the Society ofAutomotive Engineers (SAE) in 1984 as part of its Progress in TechnologySeries (No. 28). Most of the uncooled adiabatic engines produced forresearch purposes under various programs made extensive use of ceramicinsulation inserts as, for example, cylinder and combustion chamberliners, piston caps, headface plates, valve seats, valve housings andvalve guides. These programs generally examined the feasibility ofceramic lined adiabatic engines, and yttria partially-stabilisedzirconia (PSZ) was considered to be a particularly promising ceramic forthe purpose. The research programs contributed significantly to advancedengine design, but the reality is that there is today no successfuladiabatic production engine. The principal problems encountered haveincluded a short ceramic life, an inability to identify lubricants whichperformed satisfactorily at the high temperatures involved, an inabilityto obtain greater expansion energy within the cylinder and hence theneed to extract energy from the exhaust gases by secondary expansion. Afurther problem was the substantial decrease in volumetric cylinderefficiency due to the heating effect of hot cylinder/combustion chambersurfaces on the incoming air charge.

Several contributors to the above cited publication, including GM,Cummins and Komatsu, conclude that it is not possible to achievepractical adiabatic engine operation without high exhaust gastemperatures, turbo-charging or super charging (preferably withintercooling) and secondary expanders. A design by Kirloskar relied onvertically aligned cylinder fins and air cooling by convection, butachieved only a low level of adiabatic operation.

At a somewhat earlier time, the use of heat-insulated members adjacentto the combustion space was proposed by Sir Harry Ricardo for severalpurposes in enhancing the performance of high speed engines. In hisclassic text, “The High Speed Internal-Combustion Engine”, Fourth Ed1953 (Blackie & Son Glasgow), Ricardo suggests the use of aheat-insulated member placed well out of the path of the entering air.He suggests that such a member would be easy to provide for in acompression swirl engine, and possibly in an induction swirl engine, ofeither the sleeve valve 4-stroke or the 2-stroke type, but could only befitted with great difficulty, or with breathing restrictions, in an openchamber poppet valve 4-stroke engine. The heat-insulated member is saidby Ricardo (at page 26 of the aforementioned text) to serve thefunctions of raising the compression temperature without reducing thedensity and, if suitably positioned and proportioned, to keep the delayperiod constant in terms of crank angle, thus allowing a fixed time ofinjection throughout the entire speed range. Ricardo further suggeststhat the heat-insulated member would also be useful because its surfacetemperature will be high enough to prevent the deposition of carbon orash, and if so placed that the jet of fuel impinges upon it, it willeliminate completely the building-up of deposits in this zone,particularly when using high ash content fuels.

In Ricardo's textbook, there is also discussion, at pages 102-115, of aheat-insulated member in the context of compression swirl compressionchambers. A particular form is illustrated in FIG. 7.13 by way of anannular heat-insulated lining for the combustion chamber wall, in thecontext of a sleeve-valve combustion chamber. In respects other than thepresence of the lining, this illustration is typical of sleeve valvedcompression-ignition engines, in that the combustion chamber was formedin the so called junkhead by a cylindrical wall substantially smaller indiameter than the main cylinder wall guiding the piston and the valvesleeve. The arrangement illustrated in FIG. 7.13 of the Ricardo textwould not be practical, however, since differential expansion betweenthe junkhead body and the liner could be expected to cause practicaldifficulties as operating temperatures varied, leading to sealing and/ormechanical and/or fatigue failures. A loss of heat insulation would thenresult, due to the annular space filling with soot and/or carbonisedoil.

In sleeve-valved compression ignition engines, the sleeves typicallyoscillated both longitudinally and circumferentially and a commonfeature of the engines was admission of the air in a manner whichgenerated a high speed revolving swirl of the air in the chamber, thusenhancing mixing and combustion. Sir Harry Ricardo described typicalswirl ratios for 4-stroke operation (ie. swirl RPM relative tocrankshaft RPM), for highest brake mean effective pressure and lowestbrake specific fuel consumption, of the order of 10.

Ricardo also developed a series of indirect injection combustionchambers, illustrated for example in his aforementioned text at FIGS.7.7 and 7.10. Engines of similar type are disclosed in British Patent1046104, in Japanese patent publication 62-051718 and German patentpublication 1476351. These indirect injection systems involved localizedswirls at the transit passage into the main chamber.

Engines having co-axial combustion chambers smaller than the mainchamber are disclosed in U.S. Pat. Nos. 3,815,566 and 5,778,849, and inJapanese patent 5-157002. In U.S. Pat. No. 3,815,566, a perforatedbaffle separates the chambers.

It is an object of the invention to provide an internal combustionengine of enhanced thermal efficiency, and in one or more embodiments,to provide an improved adiabatic engine.

SUMMARY OF THE INVENTION

The present invention provides an internal combustion engine including:

a housing and piston means that are cyclically relatively displaceablealong an axis to define a variable volume working chamber;

means to admit air and fuel to said working chamber for forming anignitable mixture after compression of the air therein; and

means to exhaust combustion products from the working chamber;

wherein said variable volume working chamber includes at least twosub-chambers mutually displaced on said axis and in communication at across section at which gas in one sub-chamber may expand at leastpartially laterally as it flows from said one sub-chamber into the othersub-chamber;

wherein said air admission means, said exhaust means and saidsub-chambers are arranged so that a swirl of gas is generated andmaintained about said axis in both of said sub-chambers during operationof the engine;

and wherein said one sub-chamber is sealed and defined laterally and atan end by integral heat resistant and/or low thermal conductivity wallstructure having a surrounding heat insulation jacket and associatedheat dissipation means, arranged so that, during operation of theengine, the surfaces of the wall structure bounding said one sub-chamberare maintained at a temperature which is substantially higher than wallsurfaces bounding said other sub-chamber.

Advantageously, said sub-chambers are arranged whereby the engineoperates in a direct injection mode.

Said fuel admission means may include a fuel injector with a flowpassage through said wall structure but preferably includes a fuelinjector mounted intimately in a complementary opening or recess in saidintegral wall structure. The fuel injector preferably includes passagesfor cooling its tip.

The flow passage is advantageously arranged to open into said workingchamber at a radius that divides the said one sub-chamber into a centralcylindrical portion and an annular outer portion, which portions are ofsubstantially equal volumes.

Said one sub-chamber is typically of mean width D and mean length L awayfrom said cross-section where gas in one sub-chamber may expand at leastpartially laterally as it flows from said one sub-chamber into the othersub-chamber. The ratio L/D is preferably 0.9 or greater. In the simplestand most preferred case, said one sub-chamber is cylindrical, ofdiameter D and axial length L. Said cross-section is preferably equal toor less than said one sub-chamber.

Passages or galleries may be provided in a main cylinder of said housingextending about said other sub-chamber, for flowing lubricanttherethrough, which lubricant is thereby effective to reduce or controltemperatures and/or temperature differences across or around saidcylinder, while being thereby heated to a desired functional viscosity.

The swirl of gas in said other sub-chamber is preferably such that thereis formed therein a swirling cooler boundary layer, preferably effectiveto cool the peripheral and end walls of said other sub-chamber.

Preferably, the swirl of gas is such that the swirl ratio in said onesub-chamber is at least 6:1, and more preferably in the range from about10:1 to about 25:1. In said other sub-chamber, the swirl ratio ispreferably at least 3:1. The swirl of gas in said one chamber may besuch that there is a radial temperature gradient in the gas flow of saidone sub-chamber, with a relatively hotter core and a relatively coolerperiphery.

In a preferred embodiment, the air admission means and the exhaust meansinclude ports in said housing, and reciprocable sleeve valve meanscontrolling the ports. Said one sub-chamber is then preferably disposedwithin junkhead means opposed to said piston means.

Preferably, the housing and ports are such as to allow no or minimalpreheating of incoming air charges by hot combustion chamber walls.

Said housing may include respective cylindrical portions laterallydefining said sub-chambers, and an annular shoulder between saidcylindrical portions opposed to said piston means. The shoulder ispreferably provided by an annular head member, and said heat dissipationmeans may include annular neck means bridged to said wall structure forreducing thermal conductance from the wall structure to the annular headmember. Said shoulder and said neck means are advantageously formedintegrally with said wall structure defining said one sub-chamber.

Preferably, in operation, the engine exhibits at least near adiabaticoperation.

In an alternative embodiment, said one sub-chamber is substantiallydefined within said piston means.

Preferably, said sub-chambers are generally axially symmetrical aboutsaid axis, which is a longitudinal generally centre line axis of saidhousing.

The invention also provides, in a further aspect, an internal combustionengine including:

a housing and piston means that are cyclically relatively displaceablealong an axis to define a variable volume working chamber;

means to admit air and fuel to said working chamber for forming anignitable mixture after compression of the air therein; and

means to exhaust combustion products from the working chamber;

wherein said variable volume working chamber includes at least twosub-chambers mutually displaced on said axis and in communication at across section at which gas in one sub-chamber may expand at leastpartially laterally as it flows from said one sub-chamber into the othersub-chamber;

wherein said one sub-chamber is of mean width D and mean length L awayfrom said cross-section, and the ratio L/D is 0.9 or greater; and

wherein said air admission means includes intake ports positioned andarranged to impart a swirl to gases in said chamber about said axis,including said laterally expanding gas flowing from said one sub-chamberinto said other sub-chamber, whereby there is formed, during operationof the engine, a swirling cooler boundary layer in said othersub-chamber and a swirling flow in said one sub-chamber, the swirl ratioof said swirling flow in said one chamber being at least 6:1, preferablyin the range 10:1 to 25:1.

The invention still further provides a method of operating an internalcombustion engine at least near adiabatically, which engine has ahousing and piston means defining a working chamber, the methodincluding:

cyclically relatively displacing said housing and piston means along anaxis to define a variable volume working chamber;

admitting air and fuel to said working chamber;

compressing the air in the working chamber to form an ignitable mixture;

causing combustion of the compressed air/fuel mixture;

exhausting gases from the working chamber including causing the gases toexpand at least partially laterally as the gases flow from onesub-chamber of said working chamber into the other sub-chamber thereof;and

generating and maintaining a swirl of gas about said axis in both ofsaid sub-chambers while the engine is operating;

wherein the wall surfaces bounding said one sub-chamber are maintainedat a temperature which is substantially higher than wall surfacesbounding said other sub-chamber.

The ignitable mixture may be ignitable e.g. by compression ignition, orby spark or glow plug ignition. The air and fuel may be mixed in theworking chamber, or partially or wholly externally of the chamber.

In general, the apparatus may perform a function other than as anengine, eg. a pump or compressor. More generally then, the inventionprovides a reciprocatory machine, including:

a housing and piston means that are cyclically relatively displaceablealong an axis to define a variable volume working chamber;

means to admit fluid to said working chamber; and

means to exhaust fluid products from the working chamber;

wherein said variable volume working chamber includes at least twosub-chambers mutually displaced on said axis and in communication at across section at which gas in one sub-chamber may expand at leastpartially laterally as it flows from said one sub-chamber into the othersub-chamber;

wherein said fluid admission means, said exhaust means and saidsub-chambers are arranged so that a swirl of fluid is generated andmaintained about said axis in both of said sub-chambers during operationof the machine;

and wherein said one sub-chamber is defined laterally and at an end by awall structure with associated heat dissipation means arranged so that,during operation of the machine, the surfaces of the wall structurebounding said one sub-chamber are maintained at a temperature which issubstantially higher than wall surfaces bounding said other sub-chamber.

Any of the relevant preferred, advantageous and optional features setout above for the engine may also be included in the reciprocatorymachine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of the working end of a 4-stroke singlecylinder sleeve-valved near-adiabatic diesel engine according to anembodiment of the present invention;

FIGS. 2 and 3 are respectively cross-sections on the lines 2—2 and 3—3in FIG. 1;

FIG. 4 is a fragmentary cross-section of the driving end of the engineof FIG. 1 showing the piston and sleeve drive linkages; and

FIGS. 5 to 8 are partial developed elevations showing various relativepositions of the inlet and exhaust ports.

PREFERRED EMBODIMENTS

The illustrated 4-stroke single cylinder sleeve-valved diesel engine 10is conventional to the extent that it includes a housing 12 consistingof a main cylinder 14 and junkhead 16, a reciprocable piston 20, and anannular valve sleeve 30 having an axis 11 that forms an axis for theengine configuration. Valve sleeve 30 is both axially andcircumferentially reciprocable along the interior surface 15 of cylinder14, while piston 20 is in turn axially reciprocable in the space definedwithin the internal cylindrical surface 31 of sleeve 30. The crown 21 ofthe piston approaches but does not quite touch an annular shoulder 41 ofjunkhead 16 (the minimum gap is commonly referred to as the squishheight s), and the piston carries sealing or piston rings 23 for sealingthe interface with sleeve 30. That part of the junkhead that protrudesconcentrically within main cylinder 14 is spaced from cylinder surface15 to define an annular recess 17 that receives the reciprocatingsleeve. The interface between the sleeve and junkhead is in turn sealedby a pair of rings 33 carried by the junkhead just outwardly of shoulder41. Piston crown 21 may include a heat insulating insert as is known.

The reciprocation of the piston with respect to the cylinder andjunkhead is effective to define a variable volume working chamber 50sealed by rings 23, 33 and comprised of two sub-chambers 52, 54.Sub-chamber 54 may be non-cylindrical or may be restricted at its mouth53 but is here a cylindrical sub-chamber defined within junkhead 16 soas to be co-axial with axis 11, of uniform diameter D and axial lengthL. For direct injection, as in the illustrated embodiment, mouth 53 istypically of a cross-section equal to the cross-section of sub-chamber54. For indirect injection, the mouth will usually be smaller incross-section than the sub-chamber 54. Sub-chamber 52 lies betweenshoulder 41 and piston crown 21, and is bounded by these surfaces and bythe inner cylindrical face 31 of valve sleeve 30, thereby also havingaxis 11 as its axis. At its smallest, sub-chamber 52 is of axial extentequal to the squish height s. It will be appreciated that thearrangement of the sub-chambers is such that the engine operates indirect injection mode.

In keeping with conventional terminology, sub-chamber 52 is hereinafterreferred to as the main chamber 52, and sub-chamber 54 as the combustionchamber 54, but it is emphasized that the latter term does not suggestthat combustion is confined to sub-chamber 54.

With reference to FIG. 4, piston 20 is driven in the usual manner fromcrankshaft 25 via crank 26 and connecting rod 27, the latter beingpivotally attached to the piston by, gudgeon pin 28. Crankshaft 25 issupported in bearings 24, while conrod 27 pivots on bearing sleeve 29carded by the crank 26. Valve sleeve 30 is driven from the crankshaft(not shown) via a sub-shaft 34, bearing 34 a, crank 35, and pin 36 fixedto the lower end of the sleeve and supported in crank 35 by aspherically mounted bearing 37.

Inlet and exhaust ports are arranged about main chamber 52 as radialopenings in cylinder 14. A preferred configuration is illustrated inFIG. 3, and in FIGS. 5 to 8. This consists of a total of five similarequiangularly spaced ports, comprising three inlet ports 60, 61, 62,symmetrically at one side of a diametral plane 63, and exhaust ports 64,65 on the other side of plane 63. Matching control ports 70-75 areprovided in sleeve 30 and the circumferential movement of the sleeve issuch as to cause a fine initial opening of the inlet ports, whereuponinlet air is directed obliquely into main chamber 52 in the direction ofthe arrows D in FIG. 3, and generates a high speed swirling effect aboutthe axis 11 of the main chamber 52. Movement of the sleeve 30 in thedirection of the arrow C will complete opening of the inlet ports bybringing control ports 70, 71, 72 into register with inlet ports 60, 61,62, but the high speed swirl already generated about main chamber 52will be maintained for the whole cycle of operation, both in mainchamber 52 and, at a higher speed, into combustion chamber 54, where theswirl is effective to enhance mixing, to shorten the ignition delayperiod, and to facilitate use of single spray injectors.

A swirl generated by oblique air entry is a known characteristic ofsleeve-valved engines, and combustion chamber swirl ratios (ie. swirlRPM versus crankshaft RPM) of the order of 8 to 10 are typicallyobserved. However, in the context of the present invention, it isthought that the swirl may have important novel effects to be furtherdescribed below.

Further detail concerning port configuration and operation, and swirlratios, is provided later in this description.

The structure of junkhead 16 will now be described in greater detail.The principal central component is an integral body 40 of a heatresistant, preferably relatively low thermal conductivity material. Asuitable such material is stainless steel but alternative materials maybe employed, eg. especially steel alloys containing nickel and/orchromium, and ceramics. Body 40 has a relatively thin-walled skirtportion 42 which defines combustion chamber 54, and an enlarged solidhead 43 which closes one end of combustion chamber 54 and provides anend wall and/or surface 44 for the combustion chamber. At the other endof body 40, about the open end of combustion chamber 54, body 40 has aflange 45 that provides the aforementioned shoulder 41 bounding mainchamber 52 and thereby forms a head plate for the main chamber.

Junkhead 16 is completed by an outer annular headcap 18 and anintermediate mounting ring 19. As can be well seen from FIG. 1, aradially inner portion of headcap 18 is fixed to one end of ring 19 andthe other end of ring 19 is fixed in turn to head plate 45, bothconnections being by respective rings of bolts, screws or studs 39.Alternatively, shrink or other well known assembly methods could beused. Assembly is completed by securing the outer part of headcap 18onto the end of main cylinder 14. The arrangement is such that headcap18 and ring 19 extend about the portions 42, 43 of heat-resistant body40, and have outer matching cylindrical surfaces positioned to defineannular space 17 to receive sleeve 30. Headcap 18 and mounting ring 19are typically formed in low-cost cast materials such as aluminium oriron. Sealing rings 33 are respectively housed in a space between aperipheral rebate in head plate 45 and a lip of mounting ring 19, and ina groove of head plate 45.

Passages or galleries 80 may be provided for circulating cooling fluidwithin headcap 18 and ring 19, but the means for dissipating heat fromheat resistant body 40 is such as to restrict the heat flow and therebyallow the interior surfaces 42 a, 44 of body 40 to achieve a much higherequilibrium temperature than is conventional in the junkhead combustionspace of sleeve-valved engines. This objective is achieved in two ways.Firstly, head plate 45 is peripherally undercut at 46 so that the mainbody of head plate 45 is linked to cylindrical body portion 42 only by arelatively narrow annular neck 47. Secondly, the undercut 46 forms withan annular space 48, between ring 19 and cylindrical body portion 42,and under head 43, an insulating air jacket or curtain which isaspirated to the exterior via a small annular gap 49 separating solidhead 43 of heat-resistant body 40 from the surrounding body of junkhead16. Alternatively annular space 48 may be filled with a suitablehigh-temperature insulating material to minimise radiant and convectedheat loss from the surface of body portion 42.

Solid head portion 43 of heat-resistant body 40 is formed with amultiply stepped opening 82 to firmly seat and complement a fuelinjector 100. In this way, fuel injector 100 is intimately mounted inthe opening 82 so as to be in a sense integral with the body 40. Thenozzle tip 102 of injector 100 may be flush with the end face 44 ofcombustion chamber 54. Alternatively, it may be set back or forward ofend face 44. Preferably, either the injector is fitted with standardinternal cooling galleries, or alternatively cooling passages areprovided in the solid head 43 of heat-resistant body 40, in order toprotect the tip passages and materials at the high temperatures involvedin this case.

The orifice of tip 102, and the axis of the injector extending parallelto the main axis 11 of the system, are centered on a radius that dividescombustion chamber 54 into an inner cylindrical portion and an outerannular portion that are of substantially equal volume. It is believedby the present applicant that this is a more favourable position for thefuel injection than the conventional position favoured by Ricardo ie.with the injector axis as close as practicable to the lateralcylindrical surface of the chamber to optimise mixing of air and fuel.

It should be noted that, the aforementioned passages or galleries 80 tocirculate cooling fluid within headcap 18 and ring 19 were provided inthe prototype as a precautionary measure to ensure that the injectortips were not overheated. Testing has shown that, in fact, correctdetail design/selection of;

(1) the injectors and their mounting within the heat resistant body 40;

(2) the L/D ratio for combustion chamber 54;

(3) the design of annular space 48 and use or choice of insulationwithin it; and

(4) headcap 18 and heat resistant body 40

will allow deletion of cooling galleries 80. As will be furtherdiscussed, this allows the engine to be designed or operated without anyspecific cooling means whatsoever other than the very small amount ofheat naturally radiated or convected from the engine's externalsurfaces.

Turning now to the operation of the engine, the 4-stroke diesel orcompression ignition cycle is generally conventional in relation tosuccessive movements of the piston and the sequence of port opening andclosing. The piston compresses gases during the compression stroke, fuelis injected and, after a delay period, combustion commences and theexpansion stroke drives the piston down. At top dead centre of thecompression stroke, piston crown 21 is close to shoulder 41 butseparated by the squish height, leaving a combustion chamber comprisingprimarily combustion chamber 54 but also a minimalist main chamber 52.The second upstroke of the piston exhausts gases through ports 64,65—with port opening controlled by longitudinal movement of the sleeve30 and port closing by circumferential movement of the sleeve—while thesecond downstroke draws in fresh air through ports 60, 61, 62: here,port opening is controlled by circumferential movement of sleeve 30 andclosing by longitudinal movement.

FIGS. 5, 6, 7 and 8 are partial developed elevations (at twice the sizeor scale of FIGS. 1 to 4) of the cylindrical inner surface 15 ofcylinder 14 and the outer surface of sleeve 30 between arrows E₁ and E₂showing the relative positions of exhaust port 64, and inlet port 62 andthe movement of exhaust port 74 and inlet port 72.

FIG. 5 is drawn with sleeve crank pin 36 at the Bottom Dead Centreposition as shown in FIG. 4.

FIG. 6 is drawn with sleeve crank pin 36 at 90° after Bottom DeadCentre.

FIG. 7 is drawn with sleeve crank pin 36 at Top Dead Centre.

FIG. 8 is drawn with sleeve crank pin 36 at 90° after Top Dead Centre.

In FIGS. 5 to 8 the sleeve ports 72 and 74 are shown in dotted or brokenoutline whereas the cylinder barrel ports 62 and 64 are shown in solidor continuous outline. The orbit or motion path of the sleeve and itsports is shown by ellipses marked 130. The major axis of ellipse 130 isof course twice the crank radius M (FIG. 4) and the minor axis isdetermined by the relationship between, or the magnitudes of, crankradius M, the lateral distance N (FIG. 4) between the main cylinder axisor centreline and the centreline of the part spherical bearing 37, andthe outside radius of sleeve 30.

In FIG. 5 sleeve inlet port 72 has uncovered the inclined “opening” edgeof cylinder barrel inlet port 62 resulting in open port area 129. Thelateral width X of open area 129 is increasing rapidly due to thecircumferential velocity component of sleeve orbit 130 being at amaximum. Similarly the lateral width Y of open area 131 is decreasingrapidly, which will result in rapid closure of exhaust ports 64 and 74.

In FIG. 6 sleeve inlet port 72 is nearly in the closed position. Thevertical height Z of open area 132 is rapidly decreasing because thevertical velocity component of sleeve orbit 130 is at a maximum. Theexhaust ports 74 and 72 are closed.

In FIG. 7 all ports are closed, the lower edges of sleeve ports 72 and74 have passed well above the junk head sealing rings 33 and piston 20is at or near Top Dead Centre on the firing stroke.

In FIG. 8 the lower edge of sleeve exhaust port 74 has uncovered theupper edge of cylinder barrel port 64. The vertical height W of openarea 133 is increasing rapidly as the vertical velocity component ofsleeve orbit 130 has once again just reached a maximum value. The inletports 62 and 72 are closed.

The illustrated preferred engine and its operation differ in importantrespects from a conventional sleeve-valved engine. Firstly, it is foundthat the primary influence of the thermal resistance of body 40 affordedby its heat resistant material and integral form, and its insulationfrom its surroundings, optimised by such devices as the narrow neck 47,temperature gradients around undercut 46 and space 48 causing acirculation of air within the jacket formed by these spaces, togetherwith secondary effects such as end-losses at face 44 and at the piston21 and the influence of incoming fresh air, combine to determine anequilibrium temperature for surfaces 42 a, 44 much higher than isconventional. Moreover, the temperature of surfaces 42 a, 44 issubstantially higher than the temperature of the wall surface of mainchamber 52. Indeed, it is thought desirable that this temperaturedifference be in the range 400° to 1000° C.

A significant preferred element of the illustrated design thatfacilitates combustion chamber performance is believed to the integralmounting of the injector body in the solid heat resistant material ofbody 40.

The high temperature in the combustion chamber 54 also further reducesthe ignition “delay period”, by providing heat to rapidly vaporise theinjected fuel droplets. This effect augments the known benefits of theswirl mentioned earlier in reducing the delay period by enhancing rapidmixing of fuel and air.

It will further be appreciated that this temperature differential can bemaintained at even higher preferred values because of the lack ofrestraint on both longitudinal and lateral expansion of body portion 42.In particular, body 40 is free to expand longitudinally outwardly toaccommodate longitudinal expansion of portion 42 as the temperature ofinternal surface 42 a rises, while the gap 49 about body 40 similarlyaccommodates lateral or radial expansion. Gap 49 will typically be about0.2 mm, and the maximum radial expansion of head portion 43 arising fromthe heated body portion 42 is thought to be somewhat less than this.

Secondly, as the expansion stroke commences, and the gas expands bothdownwardly and laterally into main chamber 52 at the cross-section 53aligned with shoulder 41, a substantial temperature differential betweencombustion chamber 54 and shoulder 41, combined with the expansion ofthe gas and the level of sustained air or gas swirl about the commonaxis 11 of the chambers 52, 54 results in a highly stable swirlingboundary layer of relatively cooler gases which follows the piston crowndown adjacent the cylindrical wall 31 of sleeve 30. This is thought tobe the explanation of the observed unusually low cylinder walltemperatures. Moreover, the incoming air charge forming a fairly highspeed swirling or spiral layer inside the bore 31 of the main chamber 52is thought itself to have a significant cooling effect on surface 31 andalso on the lower face 41 of junk head 45, during the inlet stroke. Thesteady state mean external wall temperature of cylinder 14 has beenmeasured at 100° C. above ambient with the engine working at a bmep of 7bar, despite the total absence of any forced fluid cooling by eitherwater or air. This temperature rise is substantially independent ofengine operating speed, an effect quite contrary to observation withboth conventional engines and in the development of ceramic-fittedadiabatic engines. Perhaps, this arises from the expectation that, asengine operating speed is increased, the aforementioned “inlet coolingeffect” would also increase.

It is emphasised that the mechanisms just proposed are thought to be alikely explanation of the observed effect but that the present applicantis not stating that the observed low cylinder wall temperature certainlyor solely arises from this mechanism. Other mechanisms may be involved.The swirl ratio in the combustion chamber of the illustrated engine hasbeen measured to be in the region of 9.2, but the present applicantbelieves that a swirl ratio in the combustion chamber greater than 6:1,eg. in the range 10 to 25:1 or higher, is desirable for enhancing theeffects of the invention. This is, by convention, the value measured forthe combustion chamber: it will be understood that the swirl ratiogenerated in the main chamber will be less, inversely related to theratio of the chamber diameters, although other effects willaffect/influence the exact air speed, especially adjacent peripheral andend surfaces. It is preferred that the swirl ratio in the main chamber52 be at least 3:1.

A further effect of the swirl, and a third difference from conventionalengines of this general type, that is thought to arise for the air swirlin combustion chamber 54 is a temperature gradient from a relativelyhotter core to a relatively cooler periphery. The present applicant isnot certain of the extent to which this effect occurs, if at all, but itmay further assist in maximising achievable combustion chambertemperatures.

A fourth difference lies in the proportions of the combustion chamber54. In Ricardo's book referred to above, the length to diameter ratio ofthe combustion chamber is recommended to be 0.842 and all research andproduction engines illustrated in the book have this ratio in the range0.76 to 0.88. In contrast, the present applicant prefers that the ratioL/D, where L is the axial length of combustion chamber 54 and D is theuniform diameter of combustion chamber 54, should be 0.9 or greater,preferably greater than 1.0 and advantageously substantially greater,for example of the order of 2 to 4 or greater. If combustion chamber 54is made relatively elongate, it is thought this enhances the ultimatecooling effect of the swirling stable layer adjacent cylindrical surface31. The areas of the end face 44 of the combustion chamber and of thefacing end surface of piston crown 21 are reduced relative to thelateral surface area, and so end losses are diminished. Moreover, thedistance or “throw” of the fuel spray from injector tip 102 may bereduced to less than L, whereby the lowest portion of the air incombustion chamber 54 remains cooler. Higher L relative to D alsofurther reduces the initial heating effect of the incoming air caused bycontact with hot combustion chamber surfaces and the subsequentreduction in volumetric efficiency.

The cool temperature of the main cylinder body, and the remainingenvironment, is indicative of near adiabatic operation. There is no needfor a conventional air or water cooling system and indeed none isprovided. However the low temperature of the system generally has afurther consequence: most common lubricating oils require a highertemperature than found in the crankcase of this engine to achievecorrect functional viscosity. To resolve this difficulty, advantage istaken of circulation of the lubricant for the crankcase through passagesor galleries 110 in main cylinder 14 between the inlet and exhaust ports60-62, 64, 65 primarily in order to reduce the temperature differentialbetween the inlet and exhaust ports which would otherwise give rise toexcessive “out of round” distortion at the sleeve interfaces, althoughthis latter problem could of course be met by using conventionalcirculating coolant. The secondary benefit of this configuration isheating of the oil to achieve functional viscosity.

In general, it will be seen that the arrangement is designed to allow noor minimal preheating of incoming air charges by hot combustion chamberwalls.

A well-known formula for the theoretical value of the indicated airstandard thermal efficiency (ASTE) of an ideal diesel cycle is thefollowing expression:

ASTE=1−[{T ₄ −T ₁ }/k{T ₃ −T ₂}]

where the constant k is the ratio of specific heats, in this case takento be 1.4.

The temperature parameters in this expression comprise the ambienttemperature T₁, the temperature T₂ at the conclusion of compression andimmediately prior to the commencement of combustion, the combustiontemperature T₃, and the temperature T₄ at the conclusion of expansionand the start of exhaust. For the illustrated engine at the minimumbrake specific fuel consumption point (which here, as typically,approximately coincides with maximum brake manufactured pressure) theexhaust above ambient temperature, ie. T₄−T₁, has been measuredconsistently during extensive testing as typically in the range of160°-200° C., while T₃−T₂ has been estimated by established methods ataround 1900° C.

With these values in the above expression, the ASTE was calculated to beof the order of 93%. For a conventional production diesel engine ofsimilar cylinder size to the prototype and operating at the same dutypoint, the ASTE calculates to approximately 69%. At lower duty pointsthe calculated differences in ASTE are even greater.

It will be appreciated from the above discussion that the illustratedengine has a number of operating advantages, including but not limitedto the following:

(i) Because of the described properties of heat-resistant body 40 andits environment, a high equilibrium operating temperature is attained incombustion chamber 54, and heat losses preceding, during and followingcombustion are reduced. As a further result it is possible to achievesatisfactory operation with a significantly lower compression ratio thanwould otherwise be possible.

(ii) There is minimal heat loss to the cylinder wall in the expansionstroke, an effect believed to arise by virtue of the stable high-swirlstable and lower temperature gas layer against surface 31.

(iii) There is also minimal heat loss during the compression stroke,believed to be due to the combined effect of the high-swirl gas layerand the properties of heat-resistant body 40 and its environment.

(iv) The engine thus exhibits near adiabatic operation and hence thereis no need for a conventional air or water cooling system. A prototypeengine has been designed and constructed as generally shown in FIGS. 1to 4 and throughout testing has consistently operated at or close to 95%of perfect adiabatic operation. Analysis of test results clearlyindicates that operation at close to 98% of adiabatic can be achieved.

Such near-adiabatic operation has been achieved without the necessity ofhigh operating temperatures for pistons and cylinder walls;turbocharging or supercharging; compounding; bottoming cycles; use ofceramics; any specific or conventional means of cooling the cylinderhead or barrel; or higher than normal exhaust gas temperatures andwithout secondary expanders. The absence of these features, but thepresence of near-adiabatic operation, is contrary to expectation asreported above.

This outcome is to be contrasted with a statement in Diesel EngineReference Book, eds. Challen & Baranescu, at p.107 (2nd edition 1999)that “use of an adiabatic engine would of course result in a veryconsiderable increase in exhaust temperature”.

(v) As a result of these effects, there is close adherence to theparameters required for optimum ASTE in the expression above, ie highT₃−T₂ and low T₄−T₁.

(vi) Because a sleeve-valved engine design is adopted in preference to apoppet-valved engine, not only is a high swirl ratio achieved andmaintained but a very high volumetric efficiency is achieved andmaintained despite the high operating temperature of combustion chamber54. This latter effect is due to the fact that the incoming air chargeeffectively does not come into contact with the hot combustion chamber54 until after the compression stroke has commenced i.e. after theclosure of the inlet ports and the air in the main chamber 52 starts totransfer to combustion chamber 54.

(vii) The known high mechanical efficiencies of sleeve-valved enginesare available to the system.

(viii) By arranging a thermal barrier about combustion chamber 54, andhaving a cool main cylinder, the applicant avoids or minimises problemsencountered in known or proposed ceramic-fitted adiabatic engine designsas a result of high temperatures in the cylinders, pistons and valves(typically 400 to 1000° C.), piston rings and lubricant (typically up to500° C.) and exhaust gas (up to 1000° C.).

(ix) By shortening the ignition delay period (as a result of hightemperature and high swirl in chamber 54), the overall duration of thecombustion period is shortened, and combustion more closely approximatesconstant volume (the ideal) rather than constant pressure.

(x) The high achievable swirl ratios facilitate the use of single sprayinjectors in a high L/D environment.

(xi) All of these effects combine to substantially raise the brake meaneffective pressure (bmep).

(xii) High operating speeds are achievable.

(xiii) In a conventional sleeve valve Cl engine as defined and developedby Ricardo and others over many years, an increase in air swirl ratiowould automatically cause an increase in heat transfer rate,particularly away from the combustion chamber and powerfully reduce thepossibility of adiabatic operation. In the engine described herein, thatfundamental design problem, compromise or nexus is eliminated, thusallowing the full benefits which are available from high air swirlratios.

Again, it is instructive to contrast this outcome with another statementin the aforementioned “Diesel Engine Reference Book”, at p.107, that“quiescent direct injection [combustion] chambers which have the lowestsurface areas and the lowest gas velocities give the lowest [heat]losses”.

(xiv) These benefits can be achieved without incurring the penaltieswhich would otherwise arise from add-ons such as turbocharging;supercharging; secondary expansion; bottoming cycles or the use ofceramics or high surface temperatures in the main working chamber.Furthermore no conventional cooling system using air or water isrequired.

It will of course be well understood by those skilled in the engine artthat the design of any particular engine in accordance with theinvention will require a set of compromises among the preferred elementsof the invention in order to achieve given performance criteria. Forexample, the proportions of combustion chamber 54, including its L/Dratio, will be affected by its dimensional relationship to thedimensions of main chamber 52—both in turn together determining thecompression ratio and, along with port design, the respective swirlratios for the two chambers. The value of L/D also affects otherparameters, as discussed earlier, as does the injector/s position.

In an alternative embodiment, the combustion chamber 54 could beprovided in the piston rather than in the junkhead. This would be lesssatisfactory, for example because of the increased weight of the piston,and the displacement of the gudgeon pin axis or alternatively elongationof the piston, but these disadvantages would not be insurmountable ifthe application was warranted. A further disadvantage would be the needto provide a screen or guard to prevent contact between the lubricatingoil and the hot heat-resistant body defining the combustion chamber. Inthis alternative embodiment, it would be expected that the injectorwould still be disposed within the junkhead, or within the cylinder headin an overhead valve 4-stroke or 2-stroke ported version.

The illustrated engine is a 4-stroke sleeve-valved diesel or compressionignition engine. The concepts of the invention are also applicable to4-stroke sleeve-valved spark or glow plug ignition engines, 4-strokepoppet valve engines, 2-stroke engines with sleeve valves, and/or poppetvalves and/or cylinder ports controlled by piston movement, to any ofthese engines with the combustion chamber mounted in the piston, and toany of these engines using spark or glow plug ignition with gas orliquid fuel or gas fuelled with diesel pilot ignition. It is alsoemphasised that the concepts of the invention may be combined in asingle apparatus with the variable timing sleeve-valved arrangements ofthe present applicant's Australian patent 600913.

Where poppet valves are employed instead of a sleeve valve, a suitablearrangement for generating the desired form of swirl is illustrated inFIGS. 7.5 and 7.6 of the aforementioned text by Ricardo et al (Ps100,101 of the 4th ed.)

It is further emphasised that the invention is not confined to caseswhere combustion chamber 54 is cylindrical. Any other functional shapecan be employed, including arrangements with a neck or restrictedopening into main chamber 52. Where this restriction was a significantproportion of the cross-section, the engine may operate as an indirectinjection engine.

The invention of course extends to reciprocating machines havingfunctions other than as engines, eg. as compressors or pumps.

What is claimed is:
 1. An internal combustion engine including: ahousing and piston means that are cyclically relatively displaceablealong an axis to define a variable volume working chamber; means toadmit air and fuel to said working chamber for forming an ignitablemixture after compression of the air therein; and means to exhaustcombustion products from said working chamber; wherein said variablevolume working chamber includes at least two sub-chambers substantiallyco-axial about and mutually displaced on said axis and in communicationat a cross section at which gas in one sub-chamber may expand at leastpartially laterally as it flows from said sub-chamber into the othersub-chamber; wherein said air admission means, said exhaust means andsaid sub-chambers are arranged so that a swirl of gas is generated andmaintained about said axis in both of said sub-chambers during operationof the engine; and wherein said one sub-chamber is sealed and definedlaterally and at an end by integral heat resistant or low thermalconductivity wall structure having a lateral exterior, a heat insulationjacket about substantially the whole of said lateral exterior of saidwall structure, and associated heat dissipation means, arranged so that,during operation of the engine, surfaces of said wall structure boundingsaid one sub-chamber are maintained at a temperature which issubstantially higher than wall surfaces bounding said other sub-chamber.2. An internal combustion engine according to claim 1 wherein saidsub-chambers are arranged whereby the engine operates in a directinjection mode.
 3. An internal combustion engine according to claim 1wherein said sub-chambers are arranged whereby the engine operates in anindirect injection mode.
 4. An internal combustion engine according toclaim 1 wherein said fuel admission means includes a fuel injectormounted intimately in a complementary opening or recess in said integralwall structure.
 5. An internal combustion engine according to claim 4wherein said fuel injector includes a tip and passages for cooling thetip.
 6. An internal combustion engine according to claim 1 wherein saidfuel admission means includes a flow passage arranged to open into saidworking chamber at a radius that divides the said one sub-chamber into acentral cylindrical portion and an annular outer portion, which portionsare of substantially equal volumes.
 7. An internal combustion engineaccording to claim 1 wherein said one sub-chamber is of mean width D andmean length L away from L said cross-section, and a ratio L/D is 0.9 orgreater.
 8. An internal combustion engine according to claim 7 whereinsaid one sub-chamber is cylindrical, of diameter D and axial length L.9. An internal combustion engine according to claim 1 wherein saidcross-section is equal to or less than said one sub-chamber.
 10. Aninternal combustion engine according to claim 1 wherein said wallstructure is free to expand longitudinally and laterally with respect tosaid axis sufficiently to accommodate thermal expansion arising fromsaid temperature at the surfaces of the wall structure bounding said onesub-chamber.
 11. An internal combustion engine according to claim 1function including passages or galleries in a main cylinder of saidhousing extending about said other sub-chamber, for flowing lubricanttherethrough, which lubricant is thereby effective to reduce or controltemperatures or temperature differences across or around said cylinder,while being thereby heated to a desired functional viscosity.
 12. Aninternal combustion engine according to claim 1 wherein said swirl ofgas in said other sub-chamber is such that there is formed therein aswirling relatively cooler boundary layer.
 13. An internal combustionengine according to claim 12 wherein said cooler boundary layer iseffective to cool both peripheral and end walls of said othersub-chamber.
 14. An internal combustion engine according to claim 1wherein said swirl of gas is such that a swirl ratio in said onesub-chamber is at least 6:1.
 15. An internal combustion engine accordingto claim 14 wherein said swirl ratio is in the range from about 10:1 toabout 25:1.
 16. An internal combustion engine according to claim 1wherein said swirl of gas is such that a swirl ratio in said othersub-chamber is at least 3:1.
 17. An internal combustion engine accordingto claim 1 wherein said swirl of gas in said one chamber is such thatthere is a radial temperature gradient in a gas flow of said onesub-chamber, with a relatively hotter core and a relatively coolerperiphery.
 18. An internal combustion engine according to claim 1wherein said air admission means and said exhaust means include ports insaid housing, and reciprocable sleeve valve-means controlling the ports.19. An internal combustion engine according to claim 18 wherein said onesub-chamber is disposed within junkhead means opposed to said pistonmeans.
 20. An internal combustion engine according to claim 18 whereinsaid housing and ports are configured so as to allow at most minimalpreheating of incoming air charges by hot combustion chamber walls. 21.An internal combustion engine according to claim 1 wherein said housingincludes respective cylindrical portions laterally defining saidsub-chambers, and an annular shoulder between said cylindrical portionsopposed to said piston means.
 22. An internal combustion engineaccording to claim 21 wherein said shoulder is provided by an annularhead member.
 23. An internal combustion engine according to claim 22wherein said heat dissipation means includes annular neck means bridgedto said wall structure for reducing thermal conductance from the wallstructure to the annular head member.
 24. An internal combustion engineaccording to claim 23 wherein said shoulder and said neck means areformed integrally with said wall structure defining said onesub-chamber.
 25. An internal combustion engine according to claim 1which exhibits substantially adiabatic operation.
 26. An internalcombustion engine according to claim 1 wherein said one sub-chamber issubstantially defined within said piston means.
 27. An internalcombustion engine according to claim 1 wherein said sub-chambers aregenerally axially symmetrical about said axis, which is a longitudinalgenerally centre line axis of said housing.
 28. An internal combustionengine according to claim 1 wherein said ignitable mixture is ignitableby compression ignition.
 29. An internal combustion engine according toclaim 1 wherein said ignitable mixture is ignitable by spark or glowplug ignition.
 30. An internal combustion engine according to any claim1 wherein said air and fuel are mixed substantially wholly in saidworking chamber.
 31. An internal combustion engine according to claim 1wherein said air and fuel are mixed at least partially externally ofsaid working chamber.
 32. An internal combustion engine including: ahousing and piston means that are cyclically relatively displaceablealong an axis to define a variable volume working chamber; means toadmit air and fuel to said working chamber for forming an ignitablemixture after compression of the air therein; and means to exhaustcombustion products from said working chamber; wherein said variablevolume working chamber includes at last two sub-chambers mutuallydisplaced on said axis and in communication at a cross section at whichgas in one sub-chamber may expand at least partially laterally as itflows from said one sub-chamber into the other sub-chamber; wherein saidone sub-chamber is of mean width D and mean length L away from saidcross-section, and a ratio L/D is 0.9 or greater; and wherein said airadmission means includes intake ports positioned and arranged to imparta swirl to gases in said chamber about said axis, including saidlaterally expanding gas flowing from said one sub-chamber into saidother sub-chamber, whereby there is formed, during operation of theengine, a swirling cooler boundary layer in said other sub-chamber and aswirling flow in said one sub-chamber, a swirl ratio of said swirlingflow in said one chamber being at least 6:1.
 33. An internal combustionengine according to claim 32 wherein said cooler boundary layer iseffective to cool both peripheral and end walls of said othersub-chamber.
 34. A method of operating an internal combustion engine atleast near adiabatically, which engine has a housing and piston meansdefining a working chamber, the method including: cyclically relativelydisplacing said housing and piston means along an axis to define avariable volume working chamber; admitting air and fuel to said workingchamber; compressing the air in said working chamber to form anignitable compressed air/fuel mixture; causing combustion of saidcompressed air/fuel mixture; exhausting gases from the working chamberincluding causing the gases to expand at least partially laterally asthe gases flow from one sub-chamber of said working chamber into theother sub-chamber thereof; and generating and maintaining a swirl of gasabout said axis in both of said sub-chambers while the engine isoperating; wherein wall surfaces bounding said one sub-chamber aremaintained at a temperature which is substantially higher than wallsurfaces bounding said other sub-chamber.
 35. A reciprocatory machine,including: a housing and piston means that are cyclically relativelydisplaceable along an axis to define a variable volume working chamber;means to admit fluid to said working chamber; and means to exhaust fluidproducts from said working chamber; wherein said variable volume workingchamber includes at least two sub-chambers initially displaced on saidaxis and in communication at a cross section at which gas in onesub-chamber may expand at least partially laterally as it flows fromsaid one sub-chamber into the other sub-chamber; wherein said fluidadmission means, said exhaust means and said sub-chambers are arrangedso that a swirl of fluid is generated and maintained about said axis inboth of said sub-chambers during operation of the machine; and whereinsaid one sub-chamber is defined laterally and at an end by a wallstructure with associated heat dissipation means arranged so that,during operation of the machine, the surfaces of said wall structurebounding said one sub-chamber are maintained at a temperature which issubstantially higher than wall surfaces bounding said other sub-chamber.36. An internal combustion engine including: a housing and piston meansthat are cyclically relatively displaceable along an axis to define avariable volume working chamber; means to admit air and fuel to saidworking chamber for forming an ignitable mixture after compression ofthe air therein; and means to exhaust combustion products from saidworking chamber; wherein said variable volume working chamber includesat least two sub-chambers mutually displaced on said axis and incommunication at a cross section at which gas in one sub-chamber mayexpand at least partially laterally as it flows from said onesub-chamber into the other sub-chamber; wherein said air admissionmeans, said exhaust means and said sub-chambers are arranged so that aswirl of gas is generated and maintained about said axis in both of saidsub-chambers during operation of the engine; and wherein said fueladmission means includes a flow passage arranged to open into saidworking chamber at a radius that divides the said one sub-chamber into acentral cylindrical portion and an annular outer portion, which portionsare of substantially equal volumes.
 37. An internal combustion engineaccording to claim 36 wherein said one sub-chamber is of mean width Dand mean length L away from said cross-section, and a ratio L/D is 0.9or greater.
 38. An internal combustion engine according to claim 37wherein said one sub-chamber is cylindrical, of diameter D and axiallength L.
 39. An internal combustion engine according to claim 36wherein said cross-section is equal to or less than said onesub-chamber.
 40. An internal combustion engine including: a housing andpiston means that are cyclically relatively displaceable along an axisto define a variable volume working chamber; means to admit air and fuelto said working chamber for forming an ignitable mixture aftercompression of the air therein; and means to exhaust combustion productsfrom said working chamber; wherein said variable volume working chamberincludes at least two sub-chambers mutually displaced on said axis andin communication at a cross section at which gas in one sub-chamber mayexpand at least partially laterally as it flows from said onesub-chamber into the other sub-chamber; wherein said air admissionmeans, said exhaust means and said sub-chambers are arranged so that aswirl of gas is generated and maintained about said axis in both of saidsub-chambers during operation of the engine; and wherein said swirl ofgas in said other sub-chamber is such that there is formed therein aswirling relatively cooler boundary layer.
 41. An internal combustionengine according to claim 40, wherein said cooler boundary layer iseffective to cool both peripheral and end walls of said othersub-chamber.
 42. An internal combustion engine according to claim 40wherein said swirl of gas is such that a swirl ratio in said othersub-chamber is at least 3:1.
 43. An internal combustion engineincluding: a housing and piston means that are cyclically relativelydisplaceable along an axis to define a variable volume working chamber;means to admit air and fuel to said working chamber for forming anignitable mixture after compression of the air therein; and means toexhaust combustion products from said working chamber; wherein saidvariable volume working chamber includes at least two sub-chambersmutually displaced on said axis and in communication at a cross sectionat which gas in one sub-chamber may expand at least partially laterallyas it flows from said one sub-chamber into the other sub-chamber;wherein said air admission means, said exhaust means and saidsub-chambers are arranged so that a swirl of gas is generated andmaintained about said axis in both of said sub-chambers during operationof the engine; and wherein said swirl of gas in said one chamber is suchthat there is a radial temperature gradient in the gas flow of said onesub-chamber, with a relatively hotter core and a relatively coolerperiphery.
 44. An internal combustion engine according to claim 43,wherein said swirl of gas is such that a swirl ratio in said onesub-chamber is at least 6:1.
 45. An internal combustion engine accordingto claim 44 wherein said swirl ratio is in a range from about 10:1 toabout 25:1.
 46. An internal combustion engine including: a housing andpiston means that are cyclically relatively displaceable along an axisto define a variable volume working chamber; means to admit air and fuelto said working chamber for forming an ignitable mixture aftercompression of the air therein; and means to exhaust combustion productsfrom said working chamber; wherein said variable volume working chamberincludes at least two sub-chambers mutually displaced on said axis andin communication at a cross section at which gas in one sub-chamber mayexpand at least partially laterally as it flows from said onesub-chamber into the other sub-chamber; wherein said air admissionmeans, said exhaust means and said sub-chambers are arranged so that aswirl of gas is generated and maintained about said axis in both of saidsub-chambers during operation of the engine; and wherein said onesub-chamber is of mean width D and mean length L away from saidcross-section, and a ratio L/D is 0.9 or greater.
 47. An internalcombustion engine according to claim 46 wherein said one sub-chamber iscylindrical, of diameter D and axial length L.
 48. An internalcombustion engine according to claim 46 wherein said cross-section isequal to or less than said one sub-chamber.
 49. An internal combustionengine including: a housing and piston means that are cyclicallyrelatively displaceable along an axis to define a variable volumeworking chamber; means to admit air and fuel to said working chamber forforming an ignitable mixture after compression of the air therein; andmeans to exhaust combustion products from said working chamber; whereinsaid variable volume working chamber includes at least two sub-chambersmutually displaced on said axis and in communication at a cross sectionat which gas in one sub-chamber may expand at least partially laterallyas it flows from said one sub-chamber into the other sub-chamber; andwherein said one chamber is defined by wall structure free to expandlongitudinally and laterally with respect to said axis sufficiently toaccommodate thermal expansion arising from the temperature at surfacesof said wall structure bounding said one sub-chamber.
 50. An internalcombustion engine according to claim 1, wherein said air admission meansopens into said other sub-chamber, and said air admission means, saidexhaust means and said sub-chambers-are arranged so that a swirl of gasis generated in said other sub-chamber and maintained about said axis inboth of said sub-chambers.
 51. An internal combustion engine accordingto claim 1 wherein said heat dissipation means is a gap narrower thansaid jacket for aspirating said jacket.
 52. An internal combustionengine according to claim 51 wherein said gap is an annular gap withrespect to said axis.
 53. An internal combustion engine according toclaim 50 wherein said heat dissipation means is a gap narrower than saidjacket for aspirating said jacket.
 54. An internal combustion engineaccording to claim 40 wherein said one sub-chamber is of mean width Dand mean length L away from said cross-section, and a ratio L/D is 0.9or greater.
 55. An internal combustion engine according to claim 43wherein said one sub-chamber is of mean width D and mean length L awayfrom said cross-section, and a ratio L/D is 0.9 or greater.
 56. Aninternal combustion engine according to claim 49 wherein said onesub-chamber is of mean width D and mean length L away from saidcross-section, and a ratio L/D is 0.9 or greater.
 57. An internalcombustion engine according to claim 49 wherein said wall structure isfree to expand longitudinally and laterally with respect to said axissufficiently to accommodate thermal expansion arising from saidtemperature at surfaces of said wall structure bounding said onesub-chamber.
 58. An internal combustion engine according to claim 32,wherein said swirl of gas in said other sub-chamber is such that thereis formed therein a swirling relatively cooler boundary layer.
 59. Aninternal combustion engine according to claim 36, wherein said swirl ofgas in said other sub-chamber is such that there is formed therein aswirling relatively cooler boundary layer.
 60. An internal combustionengine according to claim 43, wherein said swirl of gas in said othersub-chamber is such that there is formed therein a swirling relativelycooler boundary layer.
 61. An internal combustion engine according toclaim 46, wherein said swirl of gas in said other sub-chamber is suchthat there is formed therein a swirling relatively cooler boundarylayer.
 62. An internal combustion engine according to claim 36 whereinsaid swirl of gas is such that a swirl ratio in said one sub-chamber isat least 6:1.
 63. An internal combustion engine according to claim 40wherein said swirl of gas is such that a swirl ratio in said onesub-chamber is at least 6:1.
 64. An internal combustion engine accordingto claim 46 wherein said swirl of gas is such that a swirl ratio in saidone sub-chamber is at least 6:1.
 65. An internal combustion engineaccording to claim 32 wherein said swirl of gas is such that a swirlratio in said other sub-chamber is at least 3:1.
 66. An internalcombustion engine according to claim 36 wherein said swirl of gas issuch that a swirl ratio in said other sub-chamber is at least 3:1. 67.An internal combustion engine according to claim 43 wherein said swirlof gas is such that a swirl ratio in said other sub-chamber is at least3:1.
 68. An internal combustion engine according to claim 46 whereinsaid swirl of gas is such that a swirl ratio in said other sub-chamberis at least 3:1.
 69. An internal combustion engine according to claim 32wherein said swirl of gas in said one chamber is such that there is aradial temperature gradient in a gas flow of said one sub-chamber, witha relatively hotter core and a relatively cooler periphery.
 70. Aninternal combustion engine according to claim 36 wherein said swirl ofgas in said one chamber is such that there is a radial temperaturegradient in a gas flow of said one sub-chamber, with a relatively hottercore and a relatively cooler periphery.
 71. An internal combustionengine according to claim 40 wherein said swirl of gas in said onechamber is such that there is a radial temperature gradient in a gasflow of said one sub-chamber, with a relatively hotter core and arelatively cooler periphery.
 72. An internal combustion engine accordingto claim 46 wherein said swirl of gas in said one chamber is such thatthere is a radial temperature gradient in a gas flow of said onesub-chamber, with a relatively hotter core and a relatively coolerperiphery.
 73. An internal combustion engine according to claim 32wherein said air admission means and said exhaust means include ports insaid housing, and reciprocable sleeve valve means controlling the ports.74. An internal combustion engine according to claim 36 wherein said airadmission means and said exhaust means include ports in said housing,and reciprocable sleeve valve means controlling the ports.
 75. Aninternal combustion engine according to claim 40 wherein said airadmission means and said exhaust means include ports in said housing,and reciprocable sleeve valve means controlling the ports.
 76. Aninternal combustion engine according to claim 43 wherein said airadmission means and said exhaust means include ports in said housing,and reciprocable sleeve valve means controlling the ports.
 77. Aninternal combustion engine according to claim 46 wherein said airadmission means and said exhaust means include ports in said housing,and reciprocable sleeve valve means controlling the ports.
 78. Aninternal combustion engine according to claim 49 wherein said airadmission means and said exhaust means include ports in said housing,and reciprocable sleeve valve means controlling the ports.
 79. Aninternal combustion engine according to claim 32, wherein said airadmission means opens into said other sub-chamber, and said airadmission means, said exhaust means and said sub-chambers are arrangedso that a swirl of gas is generated in said other sub-chamber andmaintained about said axis in both said sub-chambers.
 80. An internalcombustion engine according to claim 36, wherein said air admissionmeans opens into said other sub-chamber, and said air admission means,said exhaust means and said sub-chambers are arranged so that a swirl ofgas is generated in said other sub-chamber and maintained about saidaxis in both said sub-chambers.
 81. An internal combustion engineaccording to claim 43, wherein said air admission means opens into saidother sub-chamber, and said air admission means, said exhaust means andsaid sub-chambers are arranged so that a swirl of gas is generated insaid other sub-chamber and maintained about said axis in both saidsub-chambers.
 82. An internal combustion engine according to claim 46,wherein said air admission means opens into said other sub-chamber, andsaid air admission means, said exhaust means and said sub-chambers arearranged so that a swirl of gas is generated in said other sub-chamberand maintained about said axis in both said sub-chambers.
 83. Aninternal combustion engine according to claim 32 wherein said swirlratio of said swirling flow in said one chamber is in the range 10:1 to25:1.